Electric furnace.



o. VOGEL. ELECTRIC IUBNAGE.

APPLICATION PILEI) FEBJI, 1910.

Patented Oct. 8, 1912.

Af 70/7/15 K o'r'ro voGnL, or wmnnsnonr, annum.'

mornin remmen.

Specification of Letten Intent.

Patented Oct. 8, 1912.

Application Med February 11, 1910. Serial No. 548,884.

To all whom it may conca-m' Be it known that I, O'rro VOGEL, of 14 Durlacherstrasse, Wilmersdorf, Germany, a subject of the German Emperor, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

The idea of employing a melting chamber of funnel, crucible, shaft or tubular shape in 1o electric melting furnaces, has already been developed in various directions. It has also been found that this melting chamber when. ,used as an. incandescing resistance, lby reason of its uniform Shape and thickness of Wall, affords only a uniform general heating, and that whether this heating increases as the shape and thickness of wall diminish, ,in both cases the carbon-body will be subjected more to Wear the greater the increase in temperature, and the more freely the air,

and more particularly oxygen, can'gain access. Attempts have consequently been made to shut oil' these resistance bodies as much as possible from the air by arranging them in flues that are` closed airtight or filled with neutral ases. These expedients however cause fres diiiiculties, complicate the construction of such furnaces, and render their use inconvenient. For the purpose of producing a more intense heating, it has been proposed to make the resistance bodies coarsely ranular or to mix them with flint, chalk an the like. This is successful only when the heating does not require too high .35 temperatures, because otherwise these admixtures soon reach their melting point and form with the carbon, carbids, compounds ysimilar to carbids, silicates, or borates, &c., which destroy the granular texture of the resistance body. In all those cases it is a question, not only of the permanence of these re- 'sistance bodies, but also of the action upon the substances to be melted in the furnace, which substances must above all things be kept ure. In addition to the foregoing consi erations which must be observed in every electric furnace, the following are of importance in the particular case of melting quartz and glass materials. Namely, the construction of the furnace must be ada ted to the slow heating up of the materia s in the front or preparatory portion of the furnace, to the unhlndered progressive increase l of the heat until the -materials have become completely melted in the melting chamber, and tothe further treatment of the melted mass in the collectinv chamber, otherwise a clear and perfect met cannot be produced.

The present invention is designed to satisfy all the fore oing requirements.

One form of te present invention is illustrated by way of example in the accompany ing diagrammatic drawin in which the left hand half of the figure 1s an external elevation of the furnace that is composed of the divisions I, II, III fastened together by strong bolts.

The furnace casing consists of clay or ganister; it is closed at top by a cover, and is supported at its bottomon feet 22 which may be constructed in the Aform of insulators. The upper part has a tubular extension comprising a chargin hopper 1 and a worm conveyer 2 which rops the conveyed material on to the spreading cone 3 that is mounted by means of a spoked ring over the melting chamber. It is quite immaterial and depends on circumstances Whether this conveyer is operated by hand or by power, or whether another kind of conveying means is employed. The chief thing is to take care that the whole quantity of material to be treated is not charged into the furnace at once, but that it is char ed fractionally at the rate that the melt is rawn off.

The division II contains the melting chamber which, in the present example, con sists of a funnel-sha ed shaft 4 extending through an upper p ate electrode pole 10 with a current supply terminal 13, and a lower plate electrode 11 with a current supply terminal 14. This funnel extends above the upper plate electrode 10 and is backed by a filling 8 of sand, clay, magnesia, asbestos or the like which is capable of affording a firm support to this freely projecting part that serves as the re aratory heating chamber. The backing 1s lled in from the top before the ring with the spreading cone is placed in position.

The melting chamber 4 and the several compartments III, III", III, of the collectin chamber are lined with a lining 5 of su stances whose melting points are not only considerably higher than those of the materials to be melted, but which are also not liable toform compounds with those materials. Such substances are all the rare earths whose melting points are 2200 degrees centi rade or more, and, as pure oxids, do not com ine with silicic acid, which is of exceeding importance in melting quartz.

'Such oXids are the very refractory oxids of scandium, samarium, lanthanum, lzirconium, thorium, &c., which may he used either singly or mixed together, in various proportions.

As shown, the melting chamber is composed of three layers 5, 6 and 7 the lining 5 of rare earths covering the carbon wall 6, so as' to prevent direct contact between the latter and the quartz or rock crystal. The layer '7 consists of carbid of boron, carborundum or other substance having the prop# erty when cold, of conducting electricity, even though it be only in a small degree, ini order that the layer 7 shall be able to aid the heating action of the thin carbon wall, if, from any cause, the action of the carbon wall should become injuriously affected, ori if the carbon wall should be required to con-f3 duct a very strong current. When the entire wall, composed ofthe layers 5, 6, 7, has become conducting, the melting quartz in the melting chamber has c also become conducting, so that the currentl will select the straight path through the wall to the melt in accordance with the law of least resistance. These layers which aid one another by reason of their different properties, are of very great importance `for the efficient operation of the furnace and constitute a very important part of the general construction.

The intermediate space 9y between the melting funnel and the casing of the furnace is filled with any one of the llings referred to in connection with the space 8.

VThe apertures 20 serve for the introduction of the filling, and can then be closed tight, as is also necessary in the case of the space 40' 8,v by means of say, fire clay covers which may be of conical shape or be cemented in.

y When conical covers are used, a sheet metal ring is bolted around the middle of the outside wallof the furnace body II for the purpose of keeping these conical pieces firmly together.

The lower collecting chamber III which is' divided by cross partitions into three compartments of unequal sizes, has a peculiar formation. The compartment IIIHE is the largest and serves as a collector; its bottom and its sides are provided with-heating resist-ances which are supplied jwith current through the connection 15, as indicated in dotted lines in the accompanying drawing. The bottom of the collector III is raised conically in the center for the purpose of directing the quartz flowing from the middle `of the melting funnel, toward the sides passes'between the vheating resistances 16 and 17,'and is compelled v to .iow down urider 17 toward the cooling' chamber III".

Owing to this movement of the melt and to the very intense and thorough heatin of the same by means rof the closely space resistances, the melt becomes what glassmakers term clarified. These resistances 16 and 17 not only render the melt very liquid,

but they also raise it to such a high temperature as to nearly reach its boiling point. For this reason, the melt is allowed to remain without further heating in the chamber III, whence .it is taken for workin 'It is now possible either to blow the me t by means of hot compressed air in glowing molds composed of rare earths in a carbon casing, or to pour the melt into such glowing molds, both of which operations may be done by machinery. It is also possible by applying a tubular mold or spout to the tapping hole of the chamber III", tojproduce quartz tubes adapted for use in the manufacture of quartz instruments. In this latter case, in order to insure a continuously unobstructed outiow which is often hin dered by the setting of the rapidly cooling quartz, it is necessary to provide the outflow oriiice 21 with a heating resistance for the purpose of enabling a local treatment by ythe current to be applied either constantly or only in case of necessity. If, however, it' `is desired to take the molten quartz directly lances are connected together in groups, or

in parallel, then a lower voltage and a stronger current is required. But as all the conductors of the second class, to which belon not only the rare earths, but also quartz an the materials composing glass frit, be-

4come conductors of current when the temperature reaches a certain degree, and this conductivity increases as the temperature rises from red heat and white heat, it is obvious that by means of a certain mixture of the rare earths, with a preference for certain specially favorable substances, this electrical conductivity will be increased as much as possible, so that finallythe working cul'- rent is enabled from its entry into the furnace to its exit therefrom, to pass directly through the melt by avoiding all the heating resist-ances. If therefore the interior of the furnace has become so hot that the melting funnel has become full of white hot quartz, and the collector hasbecome full of liquid material, then at this moment, the greater part of the workin current is seeking its shortest way throug the melt, and the heat- 1 itil nomme ing resistances constitute merely an unimportant shunt circuit; At the moment ofA this division of current, the resistance drops so considerabl1 that the current strength increases rapi ly, and now the continuous operation of the furnace has commenced. It will thus be seen that the rent under the two conditions of working is as follows z-Whethe furnace is cold at the commencement of working, the current flows in the direction ofv the arrow through the terminal 13 into the carbon plate 10 and through the carbon funnel 6 into the lower carbon plate 11. Thence it passes through the connections 14 and 15 to heating resistances 16 and 17, which are connected by a curved piece in the side wall, and thus through heating resistance 18, which is arranged as an annular ring to terminal 19. When the furnace is hot the current flows directly through the melt to terminals 18 and 21. It is obvious that the supply of current must be adapted to this increase in strength, and that the switching and regulating arrangements constitute anessential part of the furnace fittings. For the purpose of providing the most favorable conditions for all the switching and regulating operations, each heating resistance has its own connections which are always accessible outside the furnace and can be controlled or actuated by means of special devices so that only one person is required to attend-the furnace, since the charging of the furnace and its regulation can be elfected automatically by the working current.

Having now described my invention what I claim as new and desire to secure by Letters Patent is 1. In an electric resistance furnace for melting quartz and glass, the combination with two current terminals, of a melting chamber located between said terminals, a preparatory heating chamber located above said melting chamber for receiving the materials to be melted, a collecting chamber located below said melting chamber divided into three compartments, means for charging the materials to be melted into said preparatory heating chamber at approximately the rate at which the melted materials flow into said collecting chamber, whereby the materials to be melted are enabled to remain in said preparatory heating chamber for a protracted period exposed to the heat rising from said melting chamber, an electric heating resistance surrounding said melting chamber, and an electric heating resistance surrounding said collecting chamber, whereby the materials to be melted are heated and rapidly liquefied in said melting chamber and the liquid is'heated to a still higher temperature as it flows progressively through the three compartments of said collecting chamber, and is thereby clarified and path of the cur-A adlatpted for further manufacture, as at fo 2. In an electric resistance furnace for melting quartz and glass, the combination with two current terminals, of a melting chamber located between said terminals havving a lining of oxid of the rare metals which is refractory to the melting heat of quartz and is neutral to silicic acid with a thin backing of carbon and a layer'of carbid of boron, or carborundum, behind said backing, a preparatory heating chamber located above said melting chamber for receiving the char to be melted wherein said char is heate bythe heat rising from said meftl in chamber, a collecting chamber located be ow said melting chamber for receiving the molten material therefrom, and an electric heating resistance surrounding said collecting chamber as set forth.

3. n an electrical resistancefurnace for melting quartz and glass, the combination with two current `terminals, of a melting chamber located between said terminals, having-*a lining of oxid of the rare metals which is refractory to the melting heat of quartz and is neutral to silicic acid, a preparatory heating chamber for receiving the charge to be melted, a collecting chamber for receiving the melted charge from said melting chamber, lined with a refractory oxid of the rare metals which is neutral to silicic acid, said collecting chamber being divided by two partitions into three compartments of which the front compartment has a bottom raised conically at its center, the first of said partitions being formed as an overfiow from said front compartment into the intermediate compartment, and the second partition stopping shortl of the bottom, whereby the melted charge flowing down from said melting chamber is directed by said raised conical bottom toward said first partition over which it overflows into said intermediate compartment, and thence under said second partition into said third compartment, an electric heating resistance surrounding said melting chamber, and an electric heating resistance surrounding said collecting chamber, as set forth.

4. In an electrical resistance furnace for melting quartz and glass, the combination with two current terminals, of a melting chamber located between said terminals, having a lining of oxid of the rare metals which is refractory to the melting heat of quartz and is neutral to silicic acid, a preparatory heating chamber for receiving the charge to be melted, a collecting chamber for receiving the melted charge from said melting chamber, lined with a refractory oxid of the rare metals which is neutral to silicic acid, said collecting chamber being divided by two partitions into three compartments of which the front compartment 'thence under said second partition into said thirdf compartment, an electric heating resistance' located in said rst partition, an electric heating resistance located in said second partition, and an elect-ric heating re-y sistance surrounding said collecting chainber, and an electric heatin resistance snrrounding said inciting` cham er, as set forth.

5. In an electric resistance furnace for melting quarta and glass', the combination iwith two current terminals, Aof a' melting chambery located between said terminals, a preparatory heating chamber for receiving resistance surroundingmsaid melting chamben,l a collecting chamber for receiving the melted charge from vsaid meltin chamber, -divided by two partitions into t ree interheating resistance for heating the rst'and second of said compartments, the third coinpartment havin a covei and a tapping hole, and an electric eating resistance surround- Iii testimony whereof I aiiix my signature in presence of two witnesses.

Y .TTO VOGEL. Witnesses:

WOL'DEMAR HAUPT,

HENRY Haaren.

the charge to be melted, an electric heating 25 communicating compartments, an electric 30 ing said tapping hole and said spout, as set 35 forth. 

